Technical Field
The subject matter described herein relates to voltage regulators, and in particular to low dropout regulators.
Description of Related Art
There is an increasing demand for electronic devices to be smaller, faster, and more efficient. To meet such a demand, higher performing power supply circuits, including voltage regulators, are needed. Due to spacing constraints of portable devices, circuits for multiple functions may require multiple voltage levels on the same chip. Therefore, voltage regulators are utilized to protect circuits from fluctuations in the power supply that may occur from crosstalk or digital switching. High fluctuations in the power supply are not desirable because they may damage sensitive circuit components, disrupt biasing or prevent circuits from working.
To regulate an output voltage from a higher input voltage, a voltage regulator may compare its output voltage with a fixed reference voltage, amplify the difference, and use feedback to match the output voltage to the reference voltage. There are several types of voltage regulators, namely switching regulators, linear regulators, and cascaded regulators that comprise both switching and linear regulators in cascaded architecture. A special type of linear regulators is a low dropout (LDO) regulator, which has a characteristically low dropout voltage, the minimum voltage required across the regulator to maintain regulation.
LDO regulators are favored in portable applications, particularly mobile products that are battery powered, such as cellular phones, camera recorders and laptops. To increase battery life and efficiency, these portable electronic devices require low voltage and low quiescent current flow, which is the current required to power the internal circuitry of the LDO when the external load current is zero. Low voltage is a natural consequence of improving chip process technology that leads to higher packing densities. Thus, voltage regulators that operate at low voltages and low quiescent currents while producing precise output voltages are desirable.
Many factors have to be considered in designing an LDO regulator for optimum performance in a power supply system while reducing total system cost. These factors may include dropout voltage, quiescent current, efficiency, load transient response, power supply rejection, bandwidth and stability. These factors may be competing factors that make the design process of a high performance LDO a challenging one.